Battery cells having improved power characteristics and methods of manufacturing same

ABSTRACT

A battery cell having significantly improved capacity utilization at high discharge rates while maintaining much of the energy content and other feature advantages of typical cylindrical or prismatic alkaline cells, by implementing a novel cell construction that produces increased surface area between the anode and cathode. The cell comprises an inner electrode encapsulated by a separator and disposed within the interior space of the housing. The inner electrode comprises a substantially flat material in a folded configuration and formed such that an outer extent of the inner electrode is generally conforming to a contour defined by the interior surface of the cell housing. An outer electrode is disposed within the interior space of the housing such that it is in ionic communication with the inner electrode and in electrical communication with the first terminal of the cell housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/846,020, filed May 14, 2004, which claims priority toProvisional Application Ser. No. 60/499,545, filed on Sep. 2, 2003;Provisional Application Ser. No. 60/503,298, filed Sep. 16, 2003; andProvisional Application Ser. No. 60/513,167, filed Oct. 21, 2003, all ofwhich are incorporated herein by reference.

BACKGROUND OF INVENTION

The present invention generally relates to electrochemical batterycells. More particularly, the invention relates to electrochemicalbattery cells, such as alkaline cells, having improved power and energydelivery capability through increased surface area interface betweenelectrode components.

Alkaline batteries based on manganese dioxide cathodes and zinc anodesare widely used for consumer portable electronic applications. There isa large market for primary alkaline cells in standard cylindricalformats such as AAA, AA, C and D sizes. These products have numerousadvantages. Zinc and manganese dioxide are inexpensive, safe andenvironmentally benign and the system provides good energy density. Forthe consumer, these standard alkaline products have long offered asimple and convenient universal solution for an array of electronicproducts.

There has been a proliferation in recent years, however, of new portableelectronic devices including personal digital assistants, MP3 recordersand players, DVD players, digital cameras, or the like. There is also atrend toward smaller and lighter portable electronic devices that limitthe onboard battery size. Compared to earlier devices, such as, forexample, transistor radios, the power consumption for many of these newdevices can require higher continuous or pulse currents. Conventional oreven premium alkaline cell designs cannot efficiently deliver theirstored energy at the higher drain rates.

FIG. 1 (section A) shows the capacity that can be delivered by a premiumcommercial alkaline AA cell under five discharge conditions intended tosimulate various consumer electronics application loads (based onAmerican National Standards Institute tests, Reference ANSI C18.1M,Part1-2001). At low drain rates (radio/43 ohm discharge) the alkaline AA“bobbin” cell delivers nearly all of its theoretical capacity (about 3Ah); at intermediate loads (electronic game/250 mA discharge, motorizedtoy/3.9 ohm discharge) about two-thirds of theoretical; and atmoderately high to high drain rates (photoflash/1 Amp pulse, digitalcamera/1 Amp continuous discharge), only ¼ to ½ of theoretical capacitycan be accessed.

These inefficiencies under high rate discharge are related to internalresistance and electrochemical limitations of the conventional alkalinebobbin-cell construction. While much effort has gone into improving theenergy content of the conventional alkaline bobbin cell by optimizingthe internal packing and ionic conductivity of the electrodes, thefundamental design itself has changed little.

As shown in FIG. 2, a typical alkaline manganese dioxide-zinc bobbincell 10 comprises the following main units: a steel can 12, optionallycoated with a conductive coating on the inside of the can, defining acylindrical inner space, a manganese dioxide cathode 14 formed by aplurality of hollow cylindrical pellets 16 pressed in the can, a zincanode 18 made of an anode gel and arranged in the hollow interior of thecathode 14, and a cylindrical separator 20 separating the anode 18 fromthe cathode 14. The ionic conductivity between the anode and the cathodeis provided by the presence of potassium hydroxide, KOH, electrolyteadded into the cell in a predetermined quantity.

The can 12 is closed at the bottom, and it has a central circular pip 22serving as the positive terminal. The upper end of the can 12 ishermetically sealed by a cell closure assembly which comprises anegative cap 24 formed by a thin metal sheet, a current collector nail26 attached to the negative cap 24 and penetrating deeply into the anodegel to provide electrical contact with the anode, and a plastic top 28electrically insulating the negative cap 24 from the can 12 andseparating gas spaces formed beyond the cathode and anode structures,respectively. The material of separator 20 may consist of laminated orcomposite materials or combinations thereof. Typically separatormaterials comprise an absorbent fibrous sheet material wettable by theelectrolyte, and an insulating material being impermeable to smallparticles but retaining ionic permeability.

While the bobbin cell construction is a simple design that allows forhigh-speed, low-cost manufacturing, the surface area between the anodeand cathode in a conventional bobbin cell is limited to the geometricalsurface area of the cylinder of separator between the anode and cathode.Thus, for a bobbin cell, the anode to cathode interfacial surface area(S_(i)) constituted by the interposed straight cylinder of separator isnecessarily a fraction of the external surface area (S_(e)) formed bythe cylindrical wall of the can [(S_(i))/(S_(e))<1].

In the field of batteries, the surface area of and between theelectrodes of an electrochemical cell is understood to be an importantdesign element, since the mass transport flux of ions between anode andcathode (typically slower than electron transfer or chemical kinetics)can be a rate limiting or current limiting physical process. It is notonly the ionic conductivity and surface area between the anode andcathode that is important but also the micro-porosity and surface areainside the electrodes.

It is possible to arrange for greater electrode and interfacial areawithin a cylindrical cell. The most widely used cylindrical cell designalternative to the bobbin cell is the spirally wound or jelly-rollconstruction which is well described in the Handbook of Batteries[3^(rd) Edition, editors D. Linden and T. B. Reddy, Section 3.2.11,McGraw-Hill, 2002]. In this construction thin strips of anode andcathode with separator between them are tightly wound together. Theelectrodes can be as thin as a few tenths of a millimeter and for thespirally wound cylindrical cell the anode to cathode interfacial surfacearea can be several multiples of the external surface area formed by thecylindrical wall of the can [(S_(i))/(S_(e))>>1]. The greaterinterfacial area comes at the expense of additional complexity and costto manufacture. Spiral winding requires precision alignment of anode,cathode, and separator, with lower production rates and higher capitalequipment costs than “bobbin” construction cells. The spirally wounddesign is not typically applied to the alkaline MnO₂/Zn cell where itwould defeat the economic advantage of the materials, but is applied tomore premium electrochemical systems including rechargeable nickelcadmium (NiCd) and nickel metal hydride (NiMH) batteries, andnon-rechargeable systems such as lithium iron disulfide (LiFeS₂)batteries.

Another trade-off of the spiral wound design is the higher amount ofseparator and current collector required, which take up volume thatcould otherwise be utilized for active material. Since a standard sizecylindrical cell has a fixed volume, it is most efficiently built withmaximum active material and electrolyte in order to maximize its energycontent. In the bobbin cell, in addition to lower separator content andthick electrodes, the brass nail anode current collector and cathodecurrent collection via contact with the cylindrical container wall donot significantly intrude on the interior space.

Thus, while converting from a bobbin design to spiral wound designincreases the inter-electrode surface area and power capability, it alsoreduces the energy content of the cell. A spiral wound construction maydeliver most of its energy efficiently for discharge rates on the orderof 20 C (C refers to a current equivalent to the rated capacity of thecell in ampere-hours divided by 1 hour). Such high rate dischargecapability may be essential for applications such as power tools,however is not typically needed for consumer electronics. Even devicessuch as digital cameras typically operate at more moderate dischargerates on the order of ⅓ to 1C rate.

More costly spirally wound batteries may be over designed for manyportable applications. However, for alkaline manganese dioxide cellswith a zinc anode and potassium hydroxide electrolyte to maintain theircompetitive advantage as a universal solution for a wide range ofconsumer applications, better run time at higher drain rates is needed.Much of the recent patent literature related to the alkaline cell isaimed at addressing this issue.

In addition to material and electrode formulation strategies to improvepower capability, there have been a number of strategies to increase theinterfacial surface area between the anode and cathode throughmodifications of the conventional bobbin cell. For example, Urry in U.S.Pat. No. 5,948,561 describes the use of a bisecting conductive platecoated with cathode active material to partition a V-folded tubularseparator. Luo et al. in U.S. Pat. No. 6,261,717 and Treger et al. inU.S. Pat. No. 6,514,637 also describe the creation of multiple anodecavities that are in these cases molded into the cathode pellets. Getzin U.S. Pat. No. 6,326,102 describes a relatively more complex assemblywith two separate zinc anode structures in contact with the inner andouter contours of separator encased cathode pellets. Jurca in U.S. Pat.No. 6,074,781 and Shelekhin et al. in U.S. Pat. No. 6,482,543 describestepped interior or contoured interior surfaces of the cathode pellet.Shelekhin et al. in U.S. Pat. No. 6,482,543, Lee et al in U.S. Pat. No.6,472,099 and Luo et al. in U.S. Pat. No. 6,410,187 describe branched orlobed interior electrode structures.

All of these design strategies have limitations in the effectiveincrease in surface area that is possible and introduce additionalcomplexities that detract from the utilitarian design of theconventional bobbin cell. Some may achieve greater surface area but atthe sacrifice of a cell balance change that decreases the energycontent. Multi-cavity or multiple electrode designs introduce the needfor more complex current collection and end seals. The more complexgeometries may introduce orientation requirements and the need for morecomplex tooling and machinery for assembly. Complex geometries can makeit difficult to apply separator uniformly and consistently especially inhigh-speed production, and may necessitate unconventional approachessuch as internally applied conformal coatings.

For example, branched or lobed designs have limited ability to increasesurface area unless the lobes are made thinner which makes applyingseparator and filling uniformly with gelled anode more difficult. If thelobes or branches are not thinner and longer then not much increase insurface is provided and the cell balance may be changed to be lessefficient due to changes in relative cross-sectional area of the anodeand cathode structures. Alignment of cathode pellets and breakage ofpellets in lobed designs could make manufacture difficult.

The foregoing problems associated with typical bobbin and spirally woundelectrode configurations are not limited to cylindrical cellconfigurations. Thinner product profiles and more efficient use ofbattery compartment space are also driving a trend toward the use ofthin prismatic (rectangular) cell formats and free-form cell formats.Analogs to the bobbin and spirally wound cell constructions also existfor prismatic cells, such as, for example, those shown in the Handbookof Batteries, [3^(rd) Edition, editors D. Linden and T. B. Reddy,Section 3.2.11, McGraw-Hill, 2002]. In the simplest designs of prismaticcells, opposed unitary anode and cathode masses exchange ions across aninterposed separator boundary. As an example, U.S. patent applicationPublication No. 2003/0157403 (Shelekin et al.) describes a thinprismatic IEC 7/5 F6 size alkaline cell with unitary opposed electrodemasses in which the total interfacial area between the anode and cathodeis less than the projected cross sectional area of the cell. Thus, suchdesigns do not address the aforementioned power characteristic problems.

There are two design alternatives to increase power in a prismatic cellconfiguration. The wound cell construction can be adapted by winding thestrips of electrodes on a flattened mandrel that may then be compressedbefore placing in the cell container. Alternatively, surface area withina prismatic cell can be increased by an assembly of alternatinganode/cathode stacked electrode plates, with like electrodes connectedin parallel within the cell. Both of these methods, however, are morecomplex and costly to produce than a simple bobbin cell.

In the case of prismatic cells, additional design considerations relatedto internal pressure arise. Alkaline cell products must remain withinmaximum allowable dimensions under all anticipated conditions of use andat all states of charge. These products do incorporate a safety vent butunder a broad range of normal use conditions they are effectivelysealed. Alkaline cell container walls must therefore be sufficientlyconstructed to contain any internal pressure caused by any gasgeneration or expansion associated with the cell's electrochemistry.Design accommodations can include low gassing zinc formulations and freeinternal volume for expansion, wherein the balance of the design relieson the mechanical strength of the container.

A cylindrical container is an effective pressure vessel with uniformlydistributed hoop stresses acting to reduce radial strains and the wallthickness of cylindrical alkaline cells may be as little as 0.008″.However, the prismatic form is not as effective at accommodatinginternal pressure and non-uniform bulging may occur with maximumdeflections at the midpoint of the long wall spans. While increasing thewall thickness of the container can prevent bulging of the container,this also reduces the internal volume available for active electrodemasses.

Having described many of the shortcomings of the prior art, the presentinvention is intended to, among other things, address these as well asother shortcomings in the prior art.

SUMMARY OF INVENTION

A battery cell, such as a cylindrical or prismatic alkaline cell,exhibiting significantly improved capacity utilization at high dischargerates while maintaining much of the energy content and other featureadvantages of typical cylindrical or prismatic alkaline cells, byimplementing a cell construction that produces increased surface areabetween the anode and cathode. In accordance with the principles of thepresent invention as embodied and described herein, one particularcharacterization of the present invention comprises an electrochemicalbattery cell comprising a cell housing defining an interior space havingan interior surface, a first terminal and a second terminal. The cellfurther comprises an inner electrode encapsulated by a separator anddisposed within the interior space of the housing. The inner electrodeis in a folded configuration and is formed such that an outer extent ofthe inner electrode is generally conforming to a contour defined by theinterior surface of the cell housing. The inner electrode is inelectrical communication with the second terminal of the housing. Anouter electrode is disposed within the interior space of the housingsuch that it is in ionic communication with the inner electrode and inelectrical communication with the first terminal of the cell housing.

According to particular aspects of the present invention, the innerelectrode is in an accordion-folded configuration or in a W-shapedconfiguration; the interior surface of the housing is in electricalcommunication with the first terminal and electrical communicationbetween the outer electrode and the first terminal is established bycontact between the outer electrode and the interior surface of thehousing; and the inner electrode is an anode and the outer electrode isa cathode, wherein the first terminal has a positive polarity and thesecond terminal has a negative polarity.

According to another aspect, the inner and outer electrodes interfacewith each other to define an inter-electrode surface area (S_(i)) andthe cell housing further includes an exterior surface defining anexterior surface area (S_(e)). The ratio of the inter-electrode surfacearea to the external surface area of the housing of the battery cell(S_(i)/S_(e)) is in the range of about 2 to about 8.

According to another aspect, an electrochemical battery cell comprises acell housing defining an interior space, a first terminal and a secondterminal; and an electrode assembly disposed within the interior spaceof the housing. The electrode assembly comprises an inner electrodeencapsulated by a separator and having a folded configuration and anouter electrode having a folded configuration intermeshing with thefolded configuration of the inner electrode. The electrode assembly isformed such that an outer extent of the electrode assembly is generallyconforming to a contour defined by the interior surface of the cellhousing. The inner electrode is in electrical communication with thesecond terminal of the housing and the outer electrode is in electricalcommunication with the first terminal of the housing.

According to yet another aspect, an electrochemical battery cellcomprises a cylindrically-shaped cell housing defining an interiorspace, a first terminal and a second terminal. The cell furthercomprises an electrode assembly disposed within the interior space ofthe housing. The electrode assembly comprises a pair of outer electrodesand an inner electrode encapsulated by a separator and disposed betweenthe outer electrodes. The electrode assembly has a folded configurationsuch that each of the electrodes intermeshingly engages the other. Theelectrode assembly is formed such that an outer extent of the electrodeassembly is generally conforming to the cylindrically-shaped cellhousing. The inner electrode is in electrical communication with thesecond terminal of the housing and the outer electrode is in electricalcommunication with the first terminal of the housing.

According to yet another aspect, an electrochemical battery cellcomprises a cell housing defining an interior space, a first terminaland a second terminal. The cell further comprises an inner electrodehaving a linearly geometric configuration having a cross-sectional areasubstantially less than an exterior surface area of the inner electrodeand disposed within the interior space of the housing. The innerelectrode is encapsulated by a separator and in electrical communicationwith the second terminal of the housing. The cell further comprises anouter electrode material disposed and formed within the interior spaceof the housing such that the inner electrode is embedded therein. Theouter electrode is in ionic communication with the inner electrode andelectrical communication with the first terminal of the cell housing.

According to yet another aspect, an electrochemical battery cellcomprises a cell housing defining an interior space, a first terminaland a second terminal. The cell further comprises an electrode assemblydisposed within the interior space of the housing. The electrodeassembly comprises an inner electrode encapsulated by a separator and anouter electrode. The electrodes are intermeshed together to from aninterface and compressed such that an outer extent of the electrodeassembly is generally conforming to a contour defined by the interiorsurface of the cell housing. The inner electrode is in electricalcommunication with the second terminal of the housing and the outerelectrode is in electrical communication with the first terminal of thehousing.

Methods of manufacturing an electrochemical battery cell in accordancewith the principles of the present invention are also contemplated.According to a particular aspect of the present invention, a method ofmanufacturing an electrochemical battery cell is provided comprising thesteps of: providing a battery cell housing including an interior space,a first terminal and a second terminal; providing an inner electrodehaving a substantially flat configuration and encapsulated by aseparator; providing an outer electrode having a substantially flatconfiguration; disposing the outer electrode adjacent the innerelectrode; folding the inner and outer electrodes together into a foldedconfiguration; forming the inner electrode such that an outer extent ofthe electrodes is generally conforming to a contour defined by theinterior space of the cell housing; and disposing the electrodes withinthe interior space of the housing such that the outer electrode is inelectrical communication with the first terminal of the cell housing andthe inner electrode is in electrical communication with the secondterminal of the cell housing.

Other methods in accordance with the principles of the present inventionare contemplated as well.

The methods of manufacturing an electrochemical battery cell inaccordance with the principles of the present invention can be readilytranslated to automated high-speed production. One or more steps ofthese methods can be envisioned as replacing certain unit operations ina conventional bobbin cell manufacturing plant, with others beingsimilar to those for conventional bobbin manufacturing, whilemaintaining equivalent throughput rates.

These and other aspects of the present invention will be apparent afterconsideration of the written description, drawings and claims herein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph depicting the approximate discharge capacity in Ah forvarious ANSI type tests for a current commercial premium AA cell (priorart) and a AA cell embodiment in accordance with the present invention.

FIG. 2 is a cross-sectional elevational view of a typical cylindricalcell having a bobbin-type construction.

FIG. 3 is a graph depicting cell potential versus discharge capacity for1 Amp discharge of an embodiment in accordance with the presentinvention compared to a commercial cell of the prior art.

FIGS. 4A and 4B are cross-sectional elevational and plan views,respectively, of an embodiment of the present invention incorporating alinearly geometric inner electrode.

FIG. 5A is a cross-sectional plan view of a preferred embodimentincorporating a corrugated fold electrode assembly in accordance withthe present invention.

FIG. 5B is a partial cross-sectional elevational view of the embodimentof FIG. 5A.

FIG. 5C is an assembly view of the embodiment of FIG. 5A.

FIG. 5D is a perspective view of an electrode assembly prior toformation to fit within a housing, in accordance with the principles ofthe present invention.

FIG. 6 is a cross-sectional plan view of an embodiment in accordancewith the principles of the present invention having a corrugated foldanode embedded in a cathode material.

FIG. 7 is a schematic diagram depicting various stages in an assemblysequence in accordance with the principles of the present invention.

FIG. 8 is a schematic diagram depicting an assembly in accordance withthe principles of the present invention.

FIG. 9 is a schematic diagram depicting an assembly in accordance withthe principles of the present invention.

FIG. 10 is a perspective view of an electrode assembly prior toformation to fit within a housing, in accordance with the principles ofthe present invention.

FIG. 11 is an assembly view of an embodiment in accordance with theprinciples of the present invention.

FIG. 12A is an assembly view of an inner electrode assembly inaccordance with the principles of the present invention.

FIG. 12B is an assembly view of an outer electrode assembly inaccordance with the principles of the present invention.

FIG. 13A is a cross-sectional plan view of an embodiment of a foldedelectrode assembly in accordance with the principles of the presentinvention.

FIG. 13B is a cross-sectional plan view of the folded and formedelectrode assembly of FIG. 13A disposed within a prismatic cell housingin accordance with the principles of the present invention.

FIG. 13C is a partial perspective view of the embodiment depicted inFIG. 13B.

FIG. 14A is a cross-sectional plan view of an additional embodiment of afolded electrode assembly in accordance with the principles of thepresent invention.

FIG. 14B is a cross-sectional plan view of the folded and formedelectrode assembly of FIG. 14A disposed within a prismatic cell housingin accordance with the principles of the present invention.

FIG. 15A is a cross-sectional plan view of a pair of folded electrodeassemblies in accordance with the principles of the present invention.

FIG. 15B is a cross-sectional plan view of the folded and formedelectrode assemblies of FIG. 15A disposed within a prismatic cellhousing in accordance with the principles of the present invention.

FIG. 15C is an assembly view of the prismatic cell of FIG. 15B inaccordance with the principles of the present invention.

FIG. 15D is a perspective view of the assembled prismatic cell of FIG.15C.

FIG. 16 is a graph depicting cell discharge curves for the prismaticcells of examples 5, 6, 7 and 8 as described herein.

FIG. 17A is a cross-sectional plan view of an embodiment of a foldedelectrode assembly utilized in examples 5, 6, 7 and 8 as describedherein and in accordance with the principles of the present invention.

FIG. 17B is a cross-sectional plan view of the folded and formedelectrode assembly of FIG. 17A disposed within a prismatic cell housingin accordance with the principles of the present invention.

DETAILED DESCRIPTION

While the present invention is capable of embodiment in many differentforms, there is shown in the drawings, and will herein be described indetail, one or more specific embodiments with the understanding that thepresent disclosure is to be considered an exemplification of theprinciples of the invention and is not intended to limit the inventionto these specific embodiments.

The present invention provides a simple and effective design of abattery cell, such as a cylindrical cell, with balanced energy and powercharacteristics intermediate between the bobbin and spiral wound designsand which retains the advantages of both designs, i.e., low cost, simplemanufacturing with higher power, and high internal volume utilizationfor energy efficiency. In an embodiment, this is achieved by providing asignificant but balanced increase of anode to cathode interfacialsurface area in conjunction with thinner, high ionic conductivity,electrode structures. The present invention also provides a betterbalanced alkaline “modified” bobbin design which can be applied tovarious cell sizes including AAA, AA, C, D and others, so that highercapacity is available at higher drain rates while the favorable energystorage characteristics are retained.

An exemplification of this higher capacity benefit of the presentinvention is shown in FIG. 1, which demonstrates that the presentinvention provides a more balanced utilization profile of a AA sizecylindrical cell through increased capacity available at higher drainrates, when compared to a commercial high rate alkaline bobbin cell. Inthe example of FIG. 1, 1.5 Ah or approximately 50% of the theoreticalcapacity is delivered on the ANSI digital camera test (versus 25% for atypical conventional bobbin cell, as shown in FIG. 1 section A), whilestill achieving at least equivalent discharge capacities on moderaterate tests such as that for motorized toys (3.9 ohm). Only at the verylowest discharge rates is there any discernable loss of apparentdischarge capacity which is nevertheless still at least 70-80% of thetheoretical or typical low drain rate capacity of a conventionalalkaline bobbin cell. Thus, approximately 50% or more of the theoreticalcapacity can be obtained at a C/2 C/3 discharge rate while greater than70% of the theoretical capacity can be achieved at a C/10 dischargerate.

FIG. 3 shows a comparison of the voltage curves for a conventionalalkaline cell compared to the voltage curve under the same dischargeconditions for a cell in accordance with the principles of the presentinvention. As can be seen from FIG. 3, a cell in accordance with theprinciples of the present invention delivers approximately twice thecapacity as the conventional alkaline cell on a 1 ampere discharge to a1.0 volt cutoff, with approximately equivalent cumulative capacity outas discharge is continued over a 3.9 ohm resistor.

An effective way to characterize the ability of the invention to providea well-balanced ratio of power to energy is to perform certain tests onassembled cells. The particular test utilized consists of a series ofdischarge steps to evaluate performance at a high rate dischargefollowed by a lower rate discharge to evaluate total capacity deliverycapability. The specifics of the test for a AA size cell are: (1) acontinuous discharge at 1.0 A to a voltage cutoff of 1.0 V; (2) a 30second open circuit test; (3) a continuous discharge at 1.0 A to a 0.8 Vcutoff; (4) a 30 minute open circuit test; (5) a 3.9 Ohm discharge to0.7 V cutoff. This test is identified by the assignee of the presentinvention as a DCC4STP2 test. Other size cells may be tested similarly,but with increased or reduced current levels to reflect the capabilityof the cell size.

By performing tests of this type on cells utilizing the currentinvention and on conventional bobbin-type alkaline cells, a cleardistinction in performance can be established. A capacity delivery ratio(C_(R)) can be calculated by dividing the capacity delivered to 1.0 V at1.0 A (C_(1V)) to the total capacity delivered (C_(T)) in the test.Because the present invention utilizes an effective linearly geometricand thin inner electrode (thin meaning having a cross-sectional areasubstantially less than an exterior surface area of the innerelectrode), the capacity ratio (C_(R)) will be significantly higher thanthat achieved in conventional bobbin-type alkaline cells.

Having demonstrated some of the performance benefits over conventionalcells, the apparatus of battery cells in accordance with the principlesof the present invention will now be described. Referring now to thedrawings, in which like numerals refer to the like parts throughout theseveral figures, FIGS. 4A and 4B show an embedded inner electrodedesign, which is one possible implementation of the current invention.

Referring to FIGS. 4A and 4B, a battery cell 30 includes a cell housing31 a defining an interior space 31 b of the battery cell 30. The cellhousing 31 a includes a first terminal T1 and a second terminal T2 forfacilitating electrical connection of the cell 30 and electricalcommunication with other elements of the cell 30. The cell 30 furtherincludes an inner electrode 32, such as an anode, having a thin crosssection 32A in a linearly geometric configuration in the form of anasterisk-like shape, which utilizes a plurality of linear elements 32B.Other linearly geometric configurations can be implemented as well, suchas a cross-like shape or any other geometry comprising linear elementsor similar elements having relatively thin cross sections, i.e.,thickness dimensions of its linear elements, compared to the crosssection of the cell housing in a similar plane. In a preferredembodiment, the inner electrode has a thickness dimension substantiallyless than a dimension extending across a maximum span of a cross sectionof the cell housing taken in parallel to the thickness dimension. In apreferred embodiment, the inner electrode 32 comprises a porous solidextruded composite, which is made of active materials, conductivematerial and additives. An internally formed current collector 33 mayalso be included. The inner electrode 32 is disposed within the interiorspace 31 b of the housing 30. The inner electrode 32 is encapsulated bya separator 34 and in electrical communication with the second terminalT2 of the housing 30. An outer electrode material 35, such as a cathodematerial, is disposed and formed within the interior space 31 b of thehousing such that the inner electrode 32 is embedded therein and formingan outer electrode 36. The outer electrode 36 is in ionic communicationwith the inner electrode 32 and electrical communication with the firstterminal T1 of the cell housing 30. By embedding the inner electrode inthe outer electrode, an electrode interface is defined, which can befurther defined by an inter-electrode surface area. As shown in FIGS. 4Aand 4B, a significant and balanced increase of anode to cathodeinterfacial surface area is achieved by virtue of the electrodegeometry. Further, thinner, high ionic conductivity, electrodestructures are achieved by virtue of the thin cross sections of theinner electrode. Performance characteristics of the cell can be changedby changing the electrode geometry, which affects the interfacialsurface area between the electrodes.

Since the inner electrode 32 is a porous solid structure, the elements32B can be thinner and longer than lobes or branches of prior artdesigns. For example, in a AA cell, the inner electrode 32 may beextruded into a shape that has thin elements 32B only 0.040 0.080 inchesthick, whereas the equivalent anode diameter in a conventional AAalkaline cell would be about 0.30 inches. In this case, the innerelectrode 32 can be accessed from each side of the element 32B with themaximum effective diffusion thickness equal to one half the throughthickness. By using a solid inner electrode, not only can thinnergeometric elements be achieved by virtue of not needing to fill a narrowvoid with gel as with prior designs but the conformal coated separator34 can be applied to an external surface 37 of the inner electrode 32 bydipping or spraying rather than attempting to apply a separator to theinner surface of a complex geometry outer electrode as with priordesigns. The outer electrode 36 can then be applied around the separatorencased inner electrode 32, either external to the cell housing 31 orafter the inner electrode is disposed within the cell housing 31. In anembodiment wherein the outer electrode is applied within the housing 30,the inner electrode 32, in the form of an anode and having a linearlygeometric configuration, can be inserted into the housing 31 which canthen filled with a cathode powder and pressed to form an embedded innerelectrode 32.

Another way of achieving the embedding of the inner and outer electrodesin the cell housing would be to bend or fold the electrodes togetherexternally to the housing to form an electrode geometry, mold theelectrodes into a shape or contour conforming to the housing, and theninserting them together into the housing. Referring now to FIGS. 5A-5D,a preferred implementation of the present invention can be achieved bystarting with a simple inner electrode geometry, covering it with aseparator and surrounding it with an outer electrode material and thenforming the geometry needed to fit the cell container. As shown in FIGS.5A-5C, an electrochemical battery cell 40 includes a cell housing 41 adefining an interior space 41 b. The cell housing 41 a includes a firstterminal T1 and a second terminal T2 for facilitating electricalconnection of the cell 40 and electrical communication with otherelements of the cell 40. Referring to FIG. 5A, the cell further includesan electrode assembly 42 disposed within the interior space 41 b of thehousing 41 a. The electrode assembly 42 comprises an inner electrode 43encapsulated by a separator 44 and an outer electrode 45. The innerelectrode and the outer electrode have a thin cross section and are in afolded configuration, such as a “W” folded configuration as shown inFIG. 5D, or other folded configuration such as an accordion fold, suchthat each of the intermesh with each other. Referring to FIG. 5C, theelectrode assembly 42 is formed such that an outer extent 46 of theelectrode assembly 42 is generally conforming to a contour 47 defined byan interior surface 48 of the cell housing 40. The inner electrode 43 isin electrical communication with the second terminal T2 of the housing41 a and the outer electrode 45 is in electrical communication with thefirst terminal T1 of the housing 41 a. The interior surface 48 ispreferably in electrical communication with the first terminal T1, suchthat electrical communication between the outer electrode 45 and thefirst terminal T1 can be established by contact between the outerelectrode 45 and the interior surface 48 of the housing 41 a.

As shown in FIG. 5D, the inner electrode 43 can be wrapped or conformalcoated with the separator 44 and then sandwiched or intermingled with anouter electrode 45 to form the electrode assembly 42. The resultingelectrode assembly can then be shaped into various geometries to fitinto the housing 41 a, as shown in FIG. 5C. The interface between theinner and the outer electrodes is thus not a uniform cylinder, as withprior designs, but may be of complex shape such that the separatorcovered surface of the encapsulated inner electrode will have anexternal surface area that is greater than the surface area of aconventional bobbin cell, but less than the surface area of aconventional spirally wound cell. The encapsulated inner electrode isthinner than in a conventional bobbin cell but not as thin as in spiralwound cell. The design achieves a better balance of surface area so thatless separator and current collector is used for the encapsulatedelectrode cell than for a conventional spiral wind design therebyincreasing the volume available for active material and thus the energycontent.

In an alternate embodiment as shown in FIG. 6, the inner electrode 43and separator 44 can be embedded in an outer electrode material. In suchan embodiment, the outer electrode material can be applied within thehousing 41 a after the inner electrode 43 is disposed therein, andpressed to form an embedded inner electrode 43 within the cathodematerial. Alternatively, the inner electrode 43 and separator 44 can befolded into a folded configuration, such as a “W” configuration, andthen formed into a geometry generally conforming to the shape of thecell housing 41 a. This inner electrode 43 can then be embedded into acathode material 45 that is extruded into a geometry generallyconforming to the shape of the cell housing 41 a. The extruded cathodematerial/embedded anode results in an electrode assembly that can thenbe disposed within the cell housing 41 a.

The present invention facilitates an increase in anode to cathodeinterfacial surface area such that the ratio of inter-electrode surfacearea (S_(i)) to external surface area of the cell container or housing(S_(e)), i.e., (S_(i))/(S_(e)), may be in the range of 2 to 8 for a AAAor AA cell, (or possibly higher for larger diameter cell sizes like C orD) in order to markedly enhance high rate discharge characteristics. Theincreased interfacial area provides for a cell design with internalresistance that is a fraction of that of a bobbin cell constructed ofequivalent materials. In the examples set forth herein below, theimpedance measured at 1 KHz was 70% or less of that of a conventionalbobbin cell. Power and energy content are better balanced so that thepresent invention retains greater than 70-80% of the energy content of aconventional bobbin at moderate rate while increasing the utilization athigh power.

A particular embodiment of the present invention provides an innerelectrode that has thinner average through-thickness measure than theequivalent inner electrode in a conventional bobbin cell. By thinningthe inner electrode through-thickness the surface area can be increasedsignificantly by lengthening the cross dimension so that approximatelythe same optimal anode to cathode cell balance can be maintained. Thedecreased through-thickness dimension of the inner electrode providesshorter diffusion lengths, which further enhances power capability ofthe cell. A conventional alkaline AA size bobbin cell has a cathode ringwall thickness of approximately 0.1 to 0.15 inches and an anode corethickness of approximately 0.2 to 0.3 inches, whereas an alkaline AAcell in accordance with the principles of the present invention may havea cathode thickness of approximately 0.035 to 0.070 inches and an anodethickness of only 0.020 to 0.060 inches.

Another benefit of the present invention is the increased utilization ofthe inner electrode at high discharge rates. A conventional bobbin cellhas a low utilization at high rates because of the internal cylindricalgeometry. As the discharge of the anode proceeds radially inwards fromthe inner surface of the separator, the anode to cathode interfacialsurface area is constantly decreasing. This effectively increases thecurrent density at the discharging inner electrode surface and leads toshutdown of the discharge reaction due to transport limitations.Increasing the surface area and thinning the inner electrode maintain amore uniform current density throughout the discharge leading toincreased utilization of the inner electrode material.

In a preferred embodiment, the longitudinal dimensions of the inner andouter electrodes are approximately equal to the full internal height ofthe container minus the height required for the seal, which is typicallyat least 70% of the internal height so that the electrode compositeoccupies nearly the full length of the container and maximizes energycontent. The outer electrode is preferably formed to be in directcontact with the interior surface of the housing and current collectionfrom this outer electrode is principally via contact with and throughthe metal housing. The inner electrode is encased in separator and thenembedded in an outer electrode matrix material, or sandwiched or formedwith the inner electrode, wherein an insulated lead is brought out andthen inserted into the housing so that the outer electrode contacts theinner surface of the housing.

In the case of an alkaline MnO₂/Zinc cell, to which many of theexemplifications herein refer, the zinc anode is the inner electrode andthe MnO₂ cathode is the outer electrode which makes contact with theinterior surface of the housing for a positive polarity contact. Notethat while many examples herein consider the alkaline cell specifically,it is understood that the principles of the present invention can beapplied to other electro-chemistries and formats.

According to a particular embodiment of the present invention, analkaline manganese dioxide-zinc cell is provided comprising a manganesedioxide cathode, a zinc anode, a separator between the anode andcathode, and an aqueous alkaline potassium hydroxide electrolyte. Theanode has a non-circular cross section with a short diffusion lengthrelative to a conventional bobbin design anode such that the capacity ofthe active material is more distributed throughout the interior of thecross-section and cumulative cross-sectional perimeter which is morethan twice the cell housing diameter. The anode is wrapped in separatorand embedded in the cathode matrix which fills the space between theanode and the interior surface of the housing uniformly. The cell has awell-balanced ratio of power to energy and gets good capacityutilization at high discharge rate. In the case of a AA cell, this isexemplified by achieving greater than 1.2 Ah on a 1 Amp to 1 Voltdischarge test.

In a preferred embodiment, the present invention provides a cellcomprising a substantially planar or substantially flat separatorencapsulated zinc anode and one or two planar shaped cathodes that areformed into a an accordion fold shape and then the whole cathode/anodeassembly molded to fill the container.

The cathode structures are formulated such that they have the necessaryphysical integrity and electronic conductivity to permit handling inhigh speed production as well as to provide good electron transfercharacteristics from the interior of the folds to the cell containerwall. This can be accomplished by formulating the composite cathode withconductive fillers, reinforcing materials, binders or carrier webs. Aparticular means of achieving the necessary mechanical and electronicproperties may be to apply a metal foil or mesh to the outer face of thecathode mass such that this metal structure provides an electroniccontact to the interior surface of the housing and a continuouselectrical connection to the interior of the folds.

Methods of manufacturing an electrochemical battery cell in accordancewith the principles of the present invention are also contemplated, asshould be apparent from the foregoing description. According to aparticular aspect of the present invention, a method of manufacturing anelectrochemical battery cell is provided comprising the steps of: (A)providing a battery cell housing including an interior space, a firstterminal and a second terminal; (B) providing an inner electrode havinga thin and substantially flat configuration and encapsulated by aseparator; (C) providing an outer electrode having a thin andsubstantially flat configuration; (D) disposing the outer electrodeadjacent the inner electrode; (E) folding the inner and outer electrodestogether into a folded configuration; (F) forming the inner electrodesuch that an outer extent of the electrodes is generally conforming to acontour defined by the interior space of the cell housing; and (G)disposing the electrodes within the interior space of the housing suchthat the outer electrode is in electrical communication with the firstterminal of the cell housing and the inner electrode is in electricalcommunication with the second terminal of the cell housing.

According to another particular aspect of the present invention, amethod of manufacturing an electrochemical battery cell in the case offorming the outer electrode within the housing is also contemplated. Themethod comprises the steps of: (A) providing a battery cell housingincluding an interior space, a first terminal and a second terminal; (B)providing an inner electrode having a thin cross section in a linearlygeometric configuration and encapsulated by a separator; (C) disposingthe inner electrode within the interior space of the housing such thatit is in electrical communication with the second terminal of the cellhousing; (D) disposing an outer electrode material within the interiorspace of the cell housing such that the inner electrode is embeddedtherein and is in electrical communication with the first terminal ofthe housing; and (E) pressing the outer electrode material disposedwithin the interior space of the cell housing.

Other methods and variations of these particular methods arecontemplated and are considered within the scope of the presentinvention when understood by one of ordinary skill in the art afterconsideration of the descriptions herein.

FIG. 7 illustrates the sequence whereby the preferred embodiment may bemanufactured by a series of process steps from parts with simplegeometries and low orientation requirements. In FIG. 7 (Step I), aplanar cathode/separator-wrapped-anode/cathode stack is placed in aforming die, with the metal substrate on each cathode facing out fromthe stack. In FIG. 7 (Step II) and (Step III), shaped blades are pushedinto the die cavity in a manner to cause folding and shaping of thestack. FIG. 7 (Step IV) shows the final shaping operation to compressand mold the stack into a cylinder prior to insertion in the housing orcan.

In a particular embodiment in accordance with the principles of thepresent invention, a simple method of manufacturing is provided by whicha preferred embodiment is achieved. According to a particularembodiment, two cathodes are formed onto die punched metal substratesand placed adjacent to a centrally placed separator encased anodestructure. Thus positioned, the electrodes are intermingled and shapedby shaping dies applied perpendicular to the long axis of theelectrodes. The final die is a concentric clamshell that forms the outerextent of the electrodes to conform to a contour or shape of the cellhousing, such as a cylinder. After forming, the die opens slightly toallow the cylindrically formed integrated electrodes to be pushed into acell housing positioned adjacent to the forming die. After the electrodeassembly is in the housing, additional KOH electrolyte may be added tothe top of the open housing for absorption into the electrodes as itpasses to the next operation in sequence. The partially assembled cellat this stage has an approximately centrally placed insulated anode leadwire protruding from the top of the housing. This lead is passed throughthe center of a plastic bottom seal, and welded to an interior surfaceof a bottom cover, which is then oriented into its proper placement onthe seal. Cell closing and finishing operations are equivalent to aconventional bobbin cell process.

The steps that form the improved cell design of the present inventioncan be readily translated to automated high-speed production. Thisformation sequence can be envisioned as replacing certain unitoperations in a conventional bobbin cell manufacturing plant, with oneor more of the steps being similar to those for conventional bobbinmanufacturing. Cathode and gelled zinc anode mixing processes forexample are expected to be reasonably similar as for conventional bobbinmaking. Certain of the modified bobbin assembly process operations mayeven be carried out with altered forms of the basic process equipmentnow used, with equivalent throughput rates.

To demonstrate and exemplify the principles of the present invention,several examples will now be given. The following examples apply to ageneral purpose MnO₂/Zn AA cell that can provide greater runtime in adigital camera application, that is, the cell can deliver more capacityon a 1 Amp to 1 Volt discharge compared to a conventional MnO₂/Zn AAcell. In addition the energy content of the cell is not excessivelycompromised such that reasonable capacity is still available at amoderate rate (3.9 ohm) discharge. Example cells were tested with a 1Amp discharge to 0.8 Volt, recording the capacity achieved when the cellpotential reaches 1 Volt, thereby simulating the ANSI digital cameratest. After a 30 minute rest, there is an additional discharge step at3.9 ohms to 0.7 volts. The 1 Amp to 1 Volt capacity (C_(1V)), totalcapacity delivered (C_(T)), and capacity ratio (C_(R)) tabulated below,are indications of the high rate and low rate capacity utilizationefficiency. The data in Table 1 relates to the specific examplespresented and shows that the invention increases utilization on thedigital camera test while not affecting utilization on low rate tests,demonstrating the benefit of the present invention over the prior art.

TABLE 1 Example Number C_(1V) (Ah) C_(T) (Ah) C_(R) 1 1.2 2.0 0.60 2 1.11.8 0.61 3 1.2 1.9 0.63 4 1.35 2.0 0.68 Conventional premium 0.75 2.00.38 bobbin

The examples refer to AA cells in Ni-coated steel cans of standarddimensions. The cathode formulation may be of any type that is typicalof primary alkaline cells consisting of EMD (γ-MnO₂), conductive powder,and the remainder being other additives such as binders and electrolyte.The electrolyte is an aqueous alkaline solution of usually 4N to 12Npotassium hydroxide. The electrolyte may contain dissolved zinc oxide,ZnO, surfactants and other additives, so as to reduce the gassing of theactive zinc within the negative electrode.

The MnO₂ cathode premix formulation used in Examples I-VI consisted of apremix of Kerr-McGee High Drain EMD 69.4%, Acetylene Black 5.2%, KS-15Graphite 2.6%, PTFE-30 Suspension 0.4%, and 9 N KOH 22.4%, on a weightbasis. Mixing was carried out in a Readco mixer, ball mill, or othersuitable mixer. The cathode premix was further mixed in the ratio of 100g of mix to lg PTFE-30 suspension and 10 g of 9 N KOH solution in orderto improve the pasting characteristics and for adhesion to the Nisubstrate. The standard substrate was non-annealed expanded metal(Dexmet 3 Ni5-077). Seven grams of the cathode formula was pressed ontothe substrate in a Carver press to give a cathode assembly thickness ofabout 0.047 inches. There was some loss of electrolyte (approx. 0.5 1.0g) on pressing.

EXAMPLE 1

This is an example of the “embedded corrugated-fold” design as shown inFIGS. 5A-5D. In this example, a porous solid electroformed zinc isutilized as the anode. Referring generally to FIGS. 8-11 for all of theexamples, a planar electroformed zinc is utilized as an anodesubassembly 51 of approximately 1.5″W×1.625″H. The electroformed zincanode sub-assembly 51 was formed by pasting a zinc oxide/binder slurry63 onto a thin metal substrate 64 of silver or copper with an attachedinsulated lead 62 and then electroforming in an alkaline bath. The anodesub-assembly 51 was then washed and dried, and heat-sealed in a pouch ofScimat 700/70 separator 52 to form an anode assembly 55. The anode usedwas approximately 4.7 g in the dry state and 0.045 inches dry thicknessincluding substrate and lead. The dry anode assembly 55 was soaked in 9N KOH for at least one hour prior to being folded into a loosecorrugated “W” shape 53. Two planar MnO₂ cathodes coated onto aperforated metal substrate 54 and with an overlay of 9 N KOH soaked KC16absorber were placed, such that one was on each side of the anode andfolded to conform as intermeshing “W's” 56, resulting in an electrodeassembly in the form of a corrugated stack 57. The corrugated stack 57was pressed and molded into a cylindrical shape 58 in a compression diewith a 0.500 inch to 0.515 inch diameter bore prior to insertion into acell housing or can 59. The thickness of the electrode stack 57 wasadjusted so that it was not too thin to fill the can after forming ortoo thick so as become over compressed losing porosity and electrolyteon insertion into the can 59. After insertion into the can 59, a sealingbead 60 was formed in the upper part of the can 59. The anode lead 62was attached to a lid 63 and the can was closed to form a complete cell64.

EXAMPLE 2

This example illustrates the “embedded corrugated-fold” design shown inFIGS. 5A-5D, specifically utilizing pasted zinc in an anodesub-assembly. This anode is fabricated from zinc powder using anextrusion or pasting process to form an anode sheet. The anodesub-assembly was prepared by mixing powdered metallic zinc or zincalloys and zinc oxide together with a Kraton binder and Shellsolsolvent. The mixture was pasted onto a 0.002 inches thick perforatedcopper foil substrate with an attached lead and the solvent was allowedto evaporate. The sub-assembly was then wrapped in an SM700/70 separatorto form the anode assembly. The dry anode assembly was soaked in 9 N KOHfor at least one hour prior to being folded into a loose corrugated “W”shape. Two planar MnO₂ cathodes coated onto a perforated metal substrateand with an overlay of 9 N KOH soaked KC16 absorber were placed, suchthat one was on each side of the anode and folded to conform asintermeshing “W's.” The corrugated stack was pressed and molded into acylindrical shape in a compression die with a 0.500 inch to 0.515 inchdiameter bore prior to insertion into the housing or can. The thicknessof the electrode stack was adjusted so that it was not too thin to fillthe can after forming or too thick so as become over compressed losingporosity and electrolyte on insertion into the can. After insertion intothe can, a sealing bead was formed in the upper part of the can. Theanode lead was attached to the lid and the can was closed to form acomplete cell.

EXAMPLE 3

This example illustrates the “embedded corrugated-fold” design shown inFIGS. 5A-5D utilizing zinc gel to form the anode assembly. The zinc gelcomprised powdered metallic zinc or zinc alloys and optionally zincoxide together with a suitable gelling agent such as carboxymethylcellulose, polyacrylic acid, starches, and their derivatives. An anodecurrent collector with an attached lead was placed in a pouch preparedout of the Scimat SM700/79 separator and 7 g of the gel was added intothe pouch which was then heat sealed at the bottom to form the anodeassembly. Two planar MnO₂ cathodes coated onto a perforated metalsubstrate and with an overlay of 9 N KOH soaked KC16 absorber wereplaced, such that one was on each side of the anode assembly and foldedto conform as intermeshing “W's.” The corrugated stack was pressed andmolded into a cylindrical shape in a compression die with a 0.500 inchto 0.515 inch diameter bore prior to insertion into the housing or can.The thickness of the electrode stack was adjusted so that it was not toothin to fill the can after forming or too thick so as become overcompressed losing porosity and electrolyte on insertion into the can.After insertion into the can, a sealing bead was formed in the upperpart of the can. The anode lead was attached to the lid and the can wasclosed to form a complete cell.

EXAMPLE 4

This example illustrates the “embedded corrugated-fold” design shown inFIGS. 5A-5D utilizing zinc gel with added zinc fibers to form the anodeassembly. The zinc gel comprised powdered metallic zinc or zinc alloys,5% of Alltrista ⅛″ zinc fibers, and optionally zinc oxide together witha suitable gelling agent such as carboxymethyl cellulose, polyacrylicacid, starches, and their derivatives. An anode current collector withattached lead was placed in a pouch prepared out of a Scimat SM700/79separator and 7 g of the gel/fiber mix was added into the pouch whichwas then heat sealed at the bottom to form the anode assembly. Twoplanar MnO₂ cathodes coated onto a perforated metal substrate and withan overlay of 9 N KOH soaked KC16 absorber were placed, such that onewas on each side of the anode assembly and folded to conform asintermeshing “W's.” The corrugated stack was pressed and molded into acylindrical shape in a compression die with a 0.500 inch to 0.515 inchdiameter bore prior to insertion into the housing or can. The thicknessof the electrode stack was adjusted so that it was not too thin to fillthe can after forming or too thick so as become over compressed losingporosity and electrolyte on insertion into the can. After insertion intothe can, a sealing bead was formed in the upper part of the can. Theanode lead was attached to the lid and the can was closed to form acomplete cell.

Other manifestations of the “embedded corrugated-fold” design of thepresent invention are anticipated. For example the assembly and processvariables such as: anode weight, anode soak time, degree of compression,cathode formulation, cathode substrate, and cathode-to-can currentcollection can be “fine tuned” to maximize electrical performance of theembedded “W” design. Almost all of the cells were built with the 0.515inch diameter compression die which was adapted over the previousstandard 0.5 inch diameter die based largely on the clear observationthat less electrolyte is squeezed out during assembly. It is importantto retain enough electrolyte in the cell to facilitate performance.

It is also possible to vary the length of the electrodes or length andnumber of folds to provide more optimal surface area and filling of thecontainer, than given in the W-fold described in the examples. Ratherthan using two outer cathode assemblies, a single length of cathode maybe wrapped around the separator-encased anode and then folded into acorrugated structure. An alternate means to increase surface area is formultiple layers of cathode and anode to be used in the stack to becorrugated, for example: cathode/anode/cathode/anode/cathode.

PRISMATIC CELL EMBODIMENTSB

Based on the description above, it should be understood by one ofordinary skill in the art that the principles of the present inventionmay be embodied in any type of cell configuration, including prismaticor free-form cell configurations. Nevertheless, for purposes of furtherexemplification, several prismatic cell embodiments will now bedescribed in more detail.

Referring generally now to FIGS. 12A and 12B, a substantially flat innerelectrode 100 (FIG. 12A) and a substantially flat outer electrode 102(FIG. 12B) are provided. The inner electrode 100 shown in FIG. 12A isconstructed for use as an anode, which comprises an anode currentcollector 104 surrounded by zinc gel layers 106 and encapsulated by aseparator 108. An insulated electrical lead 110, which is attached tothe anode, passes through the separator 108 to facilitate electricalconnection of the inner electrode within a battery cell. The outerelectrode 102 shown in FIG. 12B is constructed as a cathode, whichcomprises a cathode material layer 112 and a current collector 114. Theouter electrode 102 includes an insulated electrical lead 116 tofacilitate electrical connection of the outer electrode within a batterycell. While the inner electrode is preferably configured as an anode andthe outer electrode is preferably configured as a cathode, such as thatshown in FIGS. 12A and 12B, it should be understood that both the innerelectrode and outer electrode can be configured as either a cathode oran anode.

The inner and outer electrodes 100 and 102 can be constructed in manydifferent shapes depending on the particular application. Preferably,the inner and outer electrodes 100 and 102 are constructed in asubstantially flat configuration having a rectilinear periphery. Theelectrodes 100 and 102 can then be formed together to fit within andconform to a particular cell housing (sometimes referred to herein as acan), such as a prismatic cell housing.

Referring to FIGS. 13A-13C, the electrodes 100 and 102 are shown foldedand formed to conform to a prismatic, or rectilinear, cell housing.Referring particularly to FIG. 13A, the electrodes 100 and 102 arepreferably folded together to create intimate contact therebetween,thereby forming an electrode assembly 120. In this particularembodiment, the electrodes 100 and 102 are folded in a W-likeconfiguration, as shown in FIG. 13A. However, as will be apparent fromother embodiments disclosed herein, the electrodes 100 and 102 can befolded together in any type of configuration providing adequate surfacearea interaction between the electrodes 100 and 102.

Referring now to FIGS. 13B and 13C, the electrodes 100 and 102 of theelectrode assembly 120 are formed such that an outer extent 122 of theouter electrode 102 is generally conforming to a contour 124 defined byan interior surface 126 of a cell housing 128. In this particularembodiment, the outer extent 122 of the outer electrode 102 is formed bypressing it to conform to a generally rectilinear contour. As shown inFIG. 13B, this forming results in substantial utilization of theinterior space of the cell housing and also results in good surfacecontact between the interior surface 126 of the cell housing and theouter electrode 102, which facilitates electrical connection of theouter electrode to a terminal of the battery cell in embodiments wherethe interior surface 126 is in electrical communication with a terminalof the battery cell. In a preferred embodiment, the outer extent 122 ofthe electrode 102 is formed such that it is substantially conforming tothe contour 124 defined by the interior surface 126 of the cell housingand making substantially void-free contact therewith, as shown in FIG.13B.

Referring to FIGS. 14A-14B, another embodiment is shown with a differentfolded configuration between the electrodes 100 and 102. Rather thanfolding the electrodes 100 and 102 in a W-like configuration as thatshown in FIG. 13A, the electrodes 100 and 102 shown in FIG. 14A arefolded in a tri-fold configuration to form an electrode assembly 130. Asshown in FIG. 14B, the electrode assembly 130 is formed such that anouter extent 132 of the outer electrode 102 is generally conforming to acontour 134 defined by an interior surface 136 of a cell housing 138. Asshown in FIG. 14B, this forming results in substantial utilization ofthe interior space of the cell housing and also results in substantiallyvoid-free surface contact between the interior surface 136 of the cellhousing and the outer electrode 102.

Referring to FIGS. 15A-15D, yet another embodiment is shown wherein afirst set of inner and outer electrodes 140 and 142 are folded togetherto create a first electrode assembly 144 and a second set of electrodes146 and 148 are folded together to create a second electrode assembly150. This two-assembly configuration facilitates use with a cell housing151 that includes one or more internal structural members 152, which areshown in FIGS. 15B and 15C. These structural members 152 are utilized toreduce deflection and bulging of the cell housing due to swelling andinternal pressure without the need for increasing wall thickness of thecell housing. The structural members 152 are preferably Nip-lated steel.These internal structural members 152 may be spot-welded to the interiorsurfaces of the housing, either before or after introduction of theelectrode assemblies, effectively reducing the beam length betweensupports. In this manner they can act in tension to reduce thedeflection and bulging of the case wall due to swelling and internalpressure. The internal members 152 do not need to be electricallyinsulated from the cathode mass, which in any case is in contact withthe interior surface of the housing. This type of design is one way thatthinner walled housings might be utilized with a corresponding increasein the energy content.

Several examples of a prismatic cell construction in accordance with thepresent invention will now be described, which illustrate some of theperformance characteristics of such cell construction. The examplesapply to a general purpose MnO₂/Zn cell in an IEC 7/5 F6 prismatic size(6 mm×17 mm×67 mm, 0.33 mm wall thickness, internal dimensions ofapproximately 15.74 mm×63.80 mm×4.95 mm) that can deliver high capacityon a 0.5 to 2 Amp discharge. In addition the energy content of the cellis not excessively compromised such that reasonable capacity is stillavailable at a low to moderate rate discharge. Example cells were testedand the data shows that the invention increases utilization at higherdischarge rates while not substantially affecting utilization on lowrate tests. FIG. 16 shows the discharge curves for each of the examples.The examples refer to cells that may be packaged in Ni-coated steel cansof standard dimensions, appropriate to the given cell formats. Thecathode formulation may be of any type that is typical of primaryalkaline cells consisting of EMD (γ-MnO₂), conductive powder, and theremainder being other additives such as binders and electrolyte. Theelectrolyte is an aqueous alkaline solution of usually 4N to 12Npotassium hydroxide. The electrolyte may contain dissolved zinc oxide(ZnO), surfactants and other additives, so as to reduce the gassing ofthe active zinc within the negative electrode.

The MnO₂ cathode formulation used in the examples consisted of a premixof Kerr-McGee High Drain EMD 72.6%, KS-15 Graphite 8.2%, PTFE-30Suspension 0.4%, and 9 N KOH 18.8%, on a weight basis. The cathodestructures are formulated such that they have the necessary physicalintegrity and electronic conductivity to permit handling in high speedproduction as well as to provide good electron transfer characteristicsfrom the interior of the folds to the cell container wall. This can beaccomplished by formulating the composite cathode with conductivefillers, reinforcing materials, binders or carrier webs. A particularmeans of achieving the necessary mechanical and electronic propertiesmay be to apply a metal foil or mesh to the outer face of the cathodemass such that this metal structure provides an electronic contact tothe container wall and a continuous electrical connection to theinterior of the folds. Mixing was carried out in a Readco mixer, ballmill, or other suitable mixer to provide suitable pastingcharacteristics for adhesion to the Ni substrate. The standard substratewas non-annealed expanded metal (Dexmet 3 Ni5-077).

In the following examples, zinc gel has was utilized to form the anodeassembly of the cells.

In all of the Examples, the longitudinal dimensions of the inner andouter electrodes are approximately equal to the full internal height ofthe container minus the height required for the seal, which is typicallyat least 70% of the internal height so that the electrode compositeoccupies nearly the full length of the container and maximizes energycontent. For the prismatic cell, the cathode weight was approximately 11g and thickness about 0.041 inches. There was some loss of electrolyte(approx. 0.5 1.0 g) on pressing.

EXAMPLE 5A

A test cell utilizing an electrode assembly of the present invention wasfabricated and tested. The zinc gel comprised powdered metallic zinc orzinc alloys and optionally zinc oxide together with a suitable gellingagent such as carboxymethyl cellulose, polyacrylic acid, starches, andtheir derivatives. A separator pouch of approx. 28 mm×62 mm prepared outof Scimat SM700/79 separator containing a tin coated steel substrate wasfilled with approximately 5 g of zinc gel formulation consisting of 65%zinc powder, 34.5% KOH and 0.5% carbopol to form the anode assembly. Aplanar MnO₂ cathode coated onto an expanded metal substrate of 60 mm×62mm was wrapped around the anode using the fold configuration shown inFIGS. 17A and 17B (anode 160, cathode 162, housing or case 164). Thecathode assembly weight was 11.11 g. Anode and cathode leads welded totheir respective substrates were brought out from opposite ends of thecase. This cell when discharged at a constant current of 500 mA to 0.8Volts yielded a capacity of 1.22 Ah.

EXAMPLE 6A

A second test cell utilizing an electrode assembly of the presentinvention was fabricated and tested. The zinc gel comprised powderedmetallic zinc or zinc alloys and optionally zinc oxide together with asuitable gelling agent such as carboxymethyl cellulose, polyacrylicacid, starches, and their derivatives. A separator pouch of approx. 28mm×62 mm prepared out of Scimat SM700/79 separator containing a tincoated steel substrate was filled with approximately 5 g of zinc gelformulation consisting of 65% zinc powder, 34.5% KOH and 0.5% Carbopolto form the anode assembly. A planar MnO₂ cathode coated onto anexpanded metal substrate of 60 mm×62 mm was wrapped around the anodeusing the fold configuration shown in FIGS. 17A and 17B. The cathodeassembly weight was 10.82 g. Anode and cathode leads welded to theirrespective substrates were brought out from opposite ends of the case.This cell when discharged at a constant current of 500 mA to 0.8 Voltsyielded a capacity of 1.25 Ah.

EXAMPLE 7A

A third test cell utilizing an electrode assembly of the presentinvention was fabricated and tested. The zinc gel comprised powderedmetallic zinc or zinc alloys and optionally zinc oxide together with asuitable gelling agent such as carboxymethyl cellulose, polyacrylicacid, starches, and their derivatives. A separator pouch of approx. 28mm×62 mm prepared out of Scimat SM700/79 separator containing a tincoated steel substrate was filled with approximately 4.5 g of zinc gelformulation consisting of 65% zinc powder, 34.5% KOH and 0.5% Carbopolto form the anode assembly. A planar MnO₂ cathode coated onto anexpanded metal substrate of 60 mm×62 mm was wrapped around the anodeusing the fold configuration shown in FIGS. 17A and 17B. The cathodeassembly weight was 10.14 g. Anode and cathode leads welded to theirrespective substrates were brought out from opposite ends of the case.This cell when discharged at a constant current of 500 mA to 0.8 Voltsyielded a capacity of 1.33 Ah.

EXAMPLE 8A

A fourth test cell utilizing an electrode assembly of the presentinvention was fabricated and tested. The zinc gel comprised powderedmetallic zinc or zinc alloys and optionally zinc oxide together with asuitable gelling agent such as carboxymethyl cellulose, polyacrylicacid, starches, and their derivatives. A separator pouch of approx. 28mm×62 mm prepared out of Scimat SM700/79 separator containing a tincoated steel substrate was filled with approximately 4.5 g of zinc gelformulation consisting of 65% zinc powder, 34.5% KOH and 0.5% Carbopolto form the anode assembly. A planar MnO cathode coated onto an expandedmetal substrate of 60 mm×62 mm was wrapped around the anode using thefold configuration shown in FIGS. 17A and 17B. The cathode assemblyweight was 11.57 g. Anode and cathode leads welded to their respectivesubstrates were brought out from opposite ends of the case. This cellwhen discharged at a constant current of 500 mA to 0.8 Volts yielded acapacity of 1.37 Ah.

The discharge voltage curves for the four example cells are illustratedin FIG. 16. In all of the examples above the capacity delivery to a 0.8V cutoff is greater than would be anticipated from a standardconstruction alkaline cell in the 7/5 F6 format. As a comparison,recently reported capacity for a prismatic alkaline cell of this sizewhen discharged at 500 mA to 0.8 V, was 1.08 Ah. Cells constructedaccording to the present invention delivered 15 30% better capacity.

Other manifestations of the design of the present invention areanticipated. For example, the assembly and process variables such as:anode weight, anode soak time, degree of compression, cathodeformulation, cathode substrate, and cathode-to-can current collectioncan be “fine tuned” to maximize electrical performance of the embedded“U” design. It is also possible to vary the length of the electrodes orlength and number of folds to provide more optimal surface area andfilling of the container, than given in the folded cells described inthe examples.

While specific embodiments have been illustrated and described herein,numerous modifications may come to mind without significantly departingfrom the spirit of the invention, and the scope of protection is onlylimited by the scope of the accompanying Claims.

1. A prismatic electrochemical battery cell comprising: a cell housingdefining an interior space having an interior surface, a first terminaland a second terminal; an inner electrode comprising a gelled materialand a current collector, the gelled material and current collector beingencapsulated by a separator and disposed within the interior space ofthe housing, the inner electrode comprising a substantially flatmaterial in a folded configuration and formed such that an outer extentof the inner electrode is generally conforming to a contour defined bythe interior surface of the cell housing, the inner electrode inelectrical communication with the second terminal of the housing; and anouter electrode disposed within the interior space of the housing suchthat it is in ionic communication with the inner electrode and inelectrical communication with the first terminal of the cell housing;wherein the interior surface of the cell housing is in communicationwith the first terminal such that contact between the interior surfaceand the outer electrode establishes electrical communication between theouter electrode and the first terminal.
 2. The battery cell of claim 1,wherein the inner electrode is an anode and the outer electrode is acathode, and wherein the first terminal has a positive polarity and thesecond terminal has a negative polarity.
 3. The battery cell of claim 2,wherein the anode comprises zinc.
 4. The battery cell of claim 2,wherein the cathode comprises manganese dioxide.
 5. A prismaticelectrochemical battery cell comprising: a cell housing defining aninterior space, a first terminal and a second terminal; and an electrodeassembly disposed within the interior space of the cell housing, theelectrode assembly comprising: an inner electrode comprising a gelledmaterial and a current collector, the gelled material and currentcollector being encapsulated by a separator; and an outer electrode inionic communication with the inner electrode; the electrodes eachcomprising a substantially flat material and folded together and formedsuch that an outer extent of the outer electrode is generally conformingto a contour defined by the interior surface of the cell housing; theinner electrode in electrical communication with the second terminal ofthe housing and the outer electrode in electrical communication with thefirst terminal of the cell housing; wherein the interior surface of thecell housing is in communication with the first terminal such thatcontact between the interior surface and the outer electrode establisheselectrical communication between the outer electrode and the firstterminal.
 6. The battery cell of claim 5, wherein the inner electrode isan anode and the outer electrode is a cathode, and wherein the firstterminal has a positive polarity and the second terminal has a negativepolarity.
 7. The battery cell of claim 6, wherein the anode compriseszinc.
 8. The battery cell of claim 6, wherein the cathode comprisesmanganese dioxide.
 9. A electrochemical battery cell comprising: a cellhousing defining an interior space having an interior surface, a firstterminal and a second terminal; at least one support member disposedwithin the interior space of the housing and in structural communicationwith the interior surface to provide support to the cell housing; and atleast two electrode assemblies disposed within the interior space of thecell housing, each of the electrode assemblies comprising: an innerelectrode comprising a gelled material and a current collector, thegelled material and current collector being encapsulated by a separator;and an outer electrode in ionic communication with the inner electrode;the electrodes each comprising a substantially flat material and foldedtogether and formed such that an outer extent of the outer electrode isgenerally conforming to a contour defined by the interior surface of thecell housing; the inner electrode in electrical communication with thesecond terminal of the housing and the outer electrode in electricalcommunication with the first terminal of the cell housing.
 10. Thebattery cell of claim 9, wherein the contour defined by the interiorsurface is generally rectilinear.
 11. The battery cell of claim 9,wherein the inner electrode is an anode and the outer electrode is acathode, and wherein the first terminal has a positive polarity and thesecond terminal has a negative polarity.
 12. The battery cell of claim11, wherein the anode comprises zinc.
 13. The battery cell of claim 11,wherein the cathode comprises manganese dioxide.
 14. A method ofmanufacturing a prismatic electrochemical battery cell, the methodcomprising the steps of: providing a battery cell housing including aninterior space, a first terminal and a second terminal; providing aninner electrode comprising a gelled material and a current collector,the gelled material and current collector being encapsulated by aseparator and having a substantially flat configuration; providing anouter electrode having a substantially flat configuration; disposing theouter electrode adjacent the inner electrode; folding the inner andouter electrodes together into a folded configuration; forming the innerelectrode such that an outer extent of the electrodes is generallyconforming to a rectilinear contour defined by the interior space of thecell housing such that when it is disposed within the housing, the cellis substantially free of voids between the outer extent of the electrodeassembly and the cell housing; and disposing the electrodes within theinterior space of the housing such that the outer electrode is inelectrical communication with the first terminal of the cell housing andthe inner electrode is in electrical communication with the secondterminal of the cell housing.